Method for charging batteries, particularly in cordless communication devices

ABSTRACT

In order to create a method with which, independently of the technology of the batteries utilized, a constant overcharging of the batteries is dependably avoided, even given a different capacity, particularly given a value deviating from the original capacity, and, thus, a long service life of the batteries can be assured, it is provided that an initial charging phase of the batteries after initial insertion into the device up to full charging is provided, that, subsequently, the batteries are at least partly discharged and a value representing the previously drawn capacity is generated at every point in time, that this generated value is compared at the beginning of a renewed charging phase with a stored base value representing the duration of the initial charging phase, and that subsequent charging phases follow whose duration is equal to that of the initial charging phase when the generated value is less than or equal to the base value or that subsequently charging phases follow whose duration is determined dependent on the generated value, said generated value, over and above this, being stored as new base value when it is higher than the original base value.

The present invention is directed to a method for charging batteries,particularly in cordless communication devices.

In many types of electrical and electronic devices that are to beoperated at least temporarily without a direct connection to the powernetwork, particularly in mobile or cordless telephones, rechargeablebatteries are mainly provided. These batteries are charged either in thefixed part of the respective device or in separate charging stations forre-use during mobile operation. A charging current matched to thebattery utilized is thereby generated via a charging energy source,usually by a charging device connected to the power network, and thischarging current is forwarded to the battery. However, particularemphasis must thereby be placed thereon that an overcharging of thebatteries not occur, this leading to power losses, particularly givenmore frequent charging, and potentially leading to destruction in theworst case.

In order to avoid the overcharging of the batteries by the chargingdevice of a cordless communication device, German Letters Patent 42 36811 has proposed that the charging voltage be measured at certain timeintervals and continuing to charge the batteries or ending the chargingdependent on the course of the voltage charging curve that indicates thecharging condition when rising, the charged condition when constant andthe overcharging condition given subsequent drop. In particular, NiMHbatteries having a significantly higher capacity than NiCd batteries arethus extremely sensitive to constant overcharging.

The exact measurement of the charging voltage curve with the requiredprecision and under changing operating conditions, however, is oftendifficult to determine. On the other hand, the knowledge of thecapacities of the batteries and their technology is a precondition forthe disturbance-free and long-term operation in other methods forcharging the batteries, so that switched batteries having a capacity andtechnology different from the original capacity and technology is notpossible. The correct display of the charging condition or, the capacityof the new batteries is also not possible with the prior methods.

German Letters Patent 43 16 471 discloses a method for determining thecharge condition of a rechargeable battery, whereby, in a measuringmode, the counter reading of an electronic counting device can bemodified corresponding to the charging and discharge current and, inaddition, is modified dependent on the actually existing residualcapacity of the battery, whereby the counting device is supplied, on theone hand, with signals corresponding to the capacity of the battery,which decreases with age, and, on the other hand, with signalscorresponding to the charged condition of the battery. The measuringmode comprises one or more adjustment cycles as well as one or moreworking cycles, whereby the adjustment cycle contains a discharge of therechargeable battery up to the final discharge voltage, a charging up tofully charged, and, subsequently, another discharging to the finaldischarge voltage of the battery for determining the remaining capacity,and whereby, following the end of an adjustment cycle, at least oneworking cycle follows that begins with a full charging of the batteryand that is followed by a discharge down to the final discharge voltageupon determination of the respective charged condition. The adjustmentand working cycles are monitored with the counting device byadministration of qualitative and quantitative measuring and controldata. In a preferred exemplary embodiment of the method, the measuringmode comprises one adjustment cycle and many working cycles with asequence of capacities, whereby each capacity is compared to that of thepreceding work cycle and the result of the comparison is stored, andwhereby the charging of the rechargeable battery in the followingworking cycle is determined by the comparison result from the precedingworking cycle.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method with which,regardless of the technology of the batteries utilizes, a constantovercharging of the batteries is dependably avoided even given differentcapacity, particularly given a value deviating from the originalcapacity and, thus, a long service life of the batteries can be assured.Further, a correct capacity display should be capable of beingadditionally automatically realized in the operated device.

This object is inventively achieved in accordance with the presentinvention in a method in that an initial charging phase of the batteriesfollowing initial insertion into the device up to full charging isprovided; in that the batteries are subsequently at least partlydischarged and a value representing the previously drawn capacity isgenerated at every point in time; in that, at the beginning of a renewedcharging phase, this generated value is compared to a stored base valuethat represents the duration of the initial charging phase; and in thatsubsequent charging phases follow the initial charging phase wherein thebatteries are at least partially charged when the generated value isless than or equal to the base value or wherein the batteries are atleast partially charged dependent on the generated value that, over andabove this, is stored as new base value when the generated value ishigher than the base value hitherto stored and the batteries have afully charged condition at the beginning of the discharge phase leadingto the generated value. As a result of this method, the charging phasesfollowing the initial charging phase can be automatically exactlymatched to the technology and capacity of the batteries utilized withoutthe user having to input any data whatsoever of the batteries or havingto implement adaptions himself, and without an overcharging of thebatteries occurring during daily operation of the device, for example, amobile radio telephone or a similar communication means. A longer anddisturbance-free operation is thus assured without the user having tomonitor the charging himself. The charging of the batteries can thenalways ensue quickly with maximum current without having to fear anovercharging. The at least partial discharging of the batteriesfollowing the initial charging phase can already advantageously occur asa result of the intended use of the device.

In an embodiment, there is provided a method for charging batteries,particularly in cordless communication devices, said method comprisingthe steps of:

inserting at least one battery into a device for a first time; aftersaid insertion, during an initial charging phase, fully charging saidbattery;

after said full charging, at least partially discharging said battery;

generating at each point in time a value representing a capacity drawnup to said partial discharging;

after said partial discharge, given a start of a renewed charging phase,comparing said generated value to a stored base value representing aduration of said initial charging phase; and

after said comparison, during subsequent charging phases following saidinitial charging phase, at least partially charging said battery whensaid generated value is one of less than or equal to said base value andwhen said generated value that, over and above this, is stored as a newbase value when said generated value is higher than said base valuehitherto stored and said batteries have a fully charged condition at abeginning of a discharge phase leading to said generated value.

In an embodiment, it is provided that the batteries are completelydischarged after the initial charging phase and a value representing thedrawn capacity is thereby generated; and in that subsequent chargingphases follow thereupon, wherein the batteries are at least partiallycharged dependent on the generated value, which is also stored as newbase value when the generated value deviates from the base value and thebatteries have a fully charged condition at the beginning of thedischarge phase leading to the generated value.

The exact capacity of the batteries with an arbitrary technology thatare utilized and an initially unknown capacity can thus be even moreprecisely automatically recognized by the device itself without the userhaving to input these data, as a result whereof an exact matching of thecharging cycles to the batteries utilized is permitted for avoidingovercharging.

For simplifying the operation of the device, in an embodiment, theduration of the initial charging phase and, thus, the base value isinitially prescribed dependent on the maximum capacity of the initiallyemployed batteries. The critical data for the standard equipment arethus prescribed, and the device can automatically control the optimumcharging of the batteries from the very outset.

In an embodiment, the base value or the value generated on the basis ofthe drawn capacity is established as the value of a recharging counter,whereby the de-incrementation thereof ensues proportionally to theproduct of charging current measured during the charging phases andtime. This incorporation of the charging current into the parametersthat are monitored when charging the batteries is necessary sincedifferent charging currents are present under different feed conditionsand this would lead to a deterioration of the balancing and, thus, ofthe charging event as well.

In an embodiment, upon employment of proven component parts and forsimple and fast adaptation of the required values, it is providedaccording to a further feature the first, predetermined base value andevery generated value of the re-charging counter to be stored isdeposited in an EEPROM.

In an embodiment, charging is carried out in a first part of the initialcharging phase, preferably 5.5 hours, with maximum current, and chargingin the remaining part of the initial charging phase is undertaken with alower current, preferably half the maximum current. Given thisgraduation, a harmful overcharging can be prevented to thefarthest-reaching extent even during the initial charging phase when thecapacity of the utilized batteries is not yet known.

In order to only enable the possibility for automatic recognition of thetechnology and the capacity of initially unknown batteries underconditions under which these data can be acquired, it is providedaccording to an advantageous version of the method that a conditionallowing the overwriting of the base value is set in the device onlywhen a complete initial charging phase has been run, the value generatedon the basis of the partial discharging of the batteries is higher thanthe base value or the value generated on the basis of the completedischarge of the batteries deviates from the base value and thegenerated value lies within predetermined limits.

In an embodiment, upon utilization of proven technologies and componentparts, it is preferably provided for this purpose that the conditionallowing the overwriting of the base value is established by an initialcharging flag that is reset in the EEPROM.

In an embodiment, in order, in addition to the dependable and automaticrecognition of the capacity of the utilized batteries without action onthe part of the user to be able to realize a dependable and exactdisplay of the capacity and of the charging condition of arbitrarybatteries that are utilized, likewise without needing any interventionon the part of the user, it is inventively provided that, in addition tothe aforementioned features, the battery voltage is determined precedingthe initial charging phase and after the initial insertion of thebattery into the device, that this identified voltage is compared to alower voltage threshold and a second, predetermined voltage value, andthat a first display condition is generated when the identified voltageis lower than the lower threshold voltage, that a second displaycondition is generated when the identified voltage is less than or equalto the second, predetermined voltage value, and that a third displaycondition is generated when the identified voltage is higher than thesecond, predetermined voltage value. An initial display of the chargingcondition that is already relatively accurate can thus be automaticallyobtained for any batteries that are utilized and without the user of thedevice having to know and input any data whatsoever of the batteries.

In an embodiment, it is thereby advantageously provided that the secondvoltage value is averaged from a predetermined voltage value thatrepresents the discharged condition of the batteries and a voltage valuestored in the EPROM that represents the maximum charging voltage of thepreviously employed batteries. Given the standard equipping of thedevice, a very exact display of the charge condition is thereby alreadyassured from the very outset.

In an embodiment, in a simple and proven way, a potentially new valuefor the maximum charging voltage of the batteries is stored in EEPROMafter the initial charging phase.

In an embodiment, a very exact display of the charge condition and, aswell, of the capacity of any arbitrary batteries introduced can beachieved without any and all necessity of inputting data on the part ofthe user when, it is provided that, following the initial chargingphase, the value that is currently generated and represents thepreviously drawn capacity is compared to the base value for the maximumcapacity to be drawn, and that a fourth display condition is generatedwhen the identified voltage is lower than the lower voltage threshold,and that, dependent on the ratio of the current, generated value to thebase value, further display conditions representing the charge conditionof the batteries are generated. Following the initial, automaticrecognition of the capacity of the batteries utilized, thus, a veryexact display of the charge condition is automatically produced.

In an embodiment, a standard subdivision of the charge condition displaythat is standard in many devices can be realized with extremely highprecision when, inventively, the first display condition is generatedduring every charging phase following the initial charging phase, whenthe current, generated value is between 0% and 33% of the base value,that the second display condition is generated when the current,generated value is between 34% and 66% of the base value, that the thirddisplay condition is generated when the current, generated value isbetween 67% and 99% of the base value, and that a fifth displaycondition is generated when the current, generated value is equal to thebase value. The value of the recharging counter in relationship to themaximum capacity of the batteries is thereby again the basis.

In an embodiment, in order to already advantageously provide theprevention of harmful overcharging of the batteries during the initialcharging phase, the charge voltage curve is monitored during everycharging phase implemented with maximum current, and the charging isended when the charging voltage over a defined time span hascontinuously dropped from a value previously achieved.

In an embodiment, in order to avoid the shut-off of the charging inoperating conditions wherein fluctuations of the charging voltage curveoccur but there is not yet any overcharging risk, it is advantageouslyprovided that the monitoring of the charging voltage curve is suspendedat the beginning of charging during a predetermined time span, givenpotential switching of the charging current and during the chargingphases following the initial charging phase.

In an embodiment, in order to achieve enhanced security against damageto the batteries, it can be additionally provided that the temperatureof the batteries is monitored during charging, and that at least twotemperature thresholds are prescribed, whereby charging is carried withfull charging current below the lower temperature threshold, charging iscarried out with half the charging current between the lower and thehigher temperature threshold, and maintenance charging, preferably withone-sixth of the full charging current, is implemented above the highertemperature threshold.

In an embodiment, each temperature threshold can be in turn divided intotwo sub-thresholds, whereby the intensity of the current of the chargingcurrent is switched in case of rising temperature of the batteries giventhe higher sub-threshold of the respective temperature threshold and incase of dropping temperature given the lower sub-threshold of therespective temperature threshold.

In an embodiment, in order to be able to realize an exact display of thedischarged condition of any batteries utilized, it is provided that thedischarge curve of the voltage is monitored, and the first displaycondition is generated when the voltage lies in a range around the valuerepresenting the discharge condition of the batteries, the gradient ofthe discharge curve exceeds a predetermined, negative value, and becamemore highly negative a predetermined plurality of times in succession,or when the lower end of the range around the value representing thedischarged condition was reached.

These and other features of the invention(s) will become clearer withreference to the following detailed description of the presentlypreferred embodiments and accompanied drawings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a timing diagram for explaining the running of an initialcharging phase.

FIG. 2 is a timing diagram that explains the capacity recognition whenthe batteries have been discharged into their discharged condition.

FIG. 3 is a timing diagram that explains the capacity recognition whenthe device was shut off before complete discharging of the batteries butthe higher drawing of capacity than the previous maximum capacity.

FIG. 4 is a timing diagram for explaining the capacity recognition whenthe batteries of the device are again recharged before completedischarging.

FIG. 5a is a timing diagram for explaining the temperature monitoring ofthe charging event for increasing temperature of the batteries.

FIG. 5b is a timing diagram corresponding to FIG. 5a but for droppingtemperature.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1 shows how an initial charging phase can be designed, for instancefor a standard equipping of a device operated with batteries. Thestandard capacity of the batteries that are provided is therebyinitially assumed, for example a capacity 1200 mAh of a NiMH cell thatis currently standard, and the duration of the initial charging phase iscalculated for this. As value representing the duration of the initialcharging phase, a recharging counter is set to a value corresponding tothe calculation of the initial charging phase and is preferably storedin an EEPROM in the device. The value of the recharging counter isdetermined such that the batteries are fully charged once in any case.This condition corresponds to section 1 of the solid line in FIG. 1,which represents the value of the recharging counter and that isinitially on the dot-dash level of the initial charging capacity. Themeaningful limitations for the maximum capacity are symbolized by brokenlines.

The initial phase of the batteries begins at 2. In order to preventharmful overcharging, the initial charging is graduated. Charging iscarried out with maximum current in a first time span, approximately 5.5hours in the specific example, whereby the recharging counter is quicklyde-incremented, as indicated by section 2-3 of the line in the diagram,and the remaining charging time, which derives from the maximum capacityand a charging factor with half the maximum charging current, whichcorresponds to the condition of section 3-4 in FIG. 1. This lattercondition can, for instance, be realized in a simple way in thatcharging is carried out with maximum current for a specific, short timespan, for example five minutes, and charging is then suspended for atime span of equal length.

The de-incrementation of the recharging counter during the chargingphases ensues proportionally to the product of charging current andtime. It is therefore also important for the correct balancing that thecharging current flowing at the battery posts is monitored and measured.Thus, different feed conditions, for instance given operation of thedevice in different countries with different power supply conditions,can lead to different charging currents. Without measuring the chargingcurrent, the balancing of the inventive method would deteriorate given achange of the intensity of the charging current; given measurement ofthe charging current, its respectively current size can be utilized forthe de-incrementation of the recharging counter.

The value of the charging current is initially determined by arithmeticaveraging, preferably only obtained by sliding averaging over thefurther course, whereby each new value is weighted with a slight part,preferably with 1/128, so that potential “mavericks” do not falsify theoverall result, for example due to load fluctuations.

When the device or the battery is not to be connected to the chargingdevice effecting the charging of the batteries immediately or not duringthe entire time, the recharging counter is incremented corresponding tothe power consumption via a corresponding counter circuit. In any case,however, a switch is made from maximum to half the charging currentafter a predetermined time span of the initial charging phase, i.e. the5.5 hours here.

At 4, finally, the fully charged condition of the batteries is achieved,which preferably can be recognized via a dU criterion, which shall beexplained later. An initial charging flag is reset in the EEPROM at theend of the initial charging phase and a switch is made such into anoperating condition wherein an automatic capacity recognition of newlyutilized batteries of different technologies and capacity is enabled.When, according to the current balancing, lower than a specific, slightpart of the maximum capacity was drawn from the battery, for examplemore than 2% of this maximum capacity, a holding current is activated at5 in FIG. 1, this preferably comprising approximately one-sixth of themaximum intensity of current.

Upon insertion of new batteries into the device, an initial display ofthe charge condition and/or of the capacity of the batteries can also beadvantageously immediately realized, this being based on the measuredbattery voltage. To that end, a discharge voltage, for example 2.28 V,determine for the batteries, on the one hand, and on the other hand, avoltage deposited in the EEPROM are employed, the latter essentiallycorresponding to a fully charged condition of the batteries. Afterinitial, preferably arithmetic averaging, i.e. after the reset, thisaverage value is compared to the measured voltage value of the batteriesand a first display is realized therefrom. Every further value of thebattery voltage is preferably in turn obtained by the sliding averagingthat was already explained above.

When the battery voltage is thereby lower than the discharge voltage, adisplay that signals the discharged condition of the batteries to theuser is realized via traditional display driver circuits and, forexample, upon employment of symbols standard for the correspondingdevices. If the battery voltage happens to be equal to or less than theabove average, then a display for signaling a charged condition of amaximum of one-third of the maximum capacity is realized, and a capacitydisplay of a maximum of two-thirds of the maximum capacity is generatedwhen the battery voltage is higher than said average. The user is thusalways in the secure range and cannot be surprised by a discharge of thebatteries but is actually more likely to be prompted to recharge tooearly at the start. Since, however, the battery voltage is not anabsolute criterion for the charged condition of a battery, the durationof the initial charge is reduced to a value lower than full charge onlyin the latter condition, for example to 60%, in order to prevent damagedue to overcharging.

When the devices then to be operated with different battery types, forinstance NiCd technology or NiMH technology with different capacities aswell, for instance 700 mAh or 1200 mAh, the newly utilized batteries arenot to be parameterized by the user and an exact matching of thecharging duration and an exact display of the capacity and/or of thecharged condition should nonetheless be realized, an automaticrecognition by the device is necessary. Given utilization of newbatteries or turn-on and turn-off, initially, a determination of chargeduration or display of charge condition can only ensue via the valuesonly stored in the EEPROM.

When, however, the following criteria are met, a capacity or displaybalance can be implemented automatically by the device:

before use of the device, the accumulator must have had a fully chargedcondition or the fully charged condition must have been displayed. Alonger use of the device with discharge of the batteries upon balancingof the power consumption must have occurred, this having proceeded up toautomatic shut-off or up to the display of the discharged condition ofthe batteries, where upon the device was connected to the chargingdevice; alternatively thereto, a new capacity can also be learned whenthe value of the recharging counter upon connection of the device withthe charging device or shut off is higher than the value of therecharging counter representing the prior maximum capacity. Finally, thenew capacity should like in a meaningful range, traditionally with alower limit of 300 mAh and an upper limit of 2000 mAh.

In order to achieve a more exact display as user information, a fourthdisplay, for instance a flashing symbol for empty batteries, and a fifthdisplay for the fully charged condition of the batteries should also beadditionally realized as user information, this likewise ensuing on thebasis of the value of the recharging counter relative to the maximumcapacity.

FIG. 2 shows a diagram that explains the recognition of a new capacitydeviating from the originally prescribed capacity when the accumulators,due to longer use of the device, reach the discharged condition. Thepoint of departure is thereby the fully charged condition of thebatteries at 11, at most only with holding charging that, for example,was achieved by a preceding, initial charging phase and that isrepresented by a minimum value of the recharging counter. The originallystored maximum capacity is again symbolized by a dot-dash line. Thesection 12 of the diagram corresponds to an active operation of thedevice with announcement incrementation of the recharging counter and,at 13, the device is in the standby mode wherein less power is consumedand the recharging counter therefore increases more slowly than in theactive condition at 12. The empty charged condition of the batteries isthen reached at 14, i.e. the accumulator voltage has dropped below thevoltage threshold of, for example, 2.28 V that signals this condition.Before the automatic shut-off of the device, the current value of therecharging counter is stored in the EEPROM representing the new maximumcapacity, this being identified by the higher level of the dot-dashline.

Since the duration of the shut-off of the device cannot be recognized, apredetermined part, preferably 10% of the maximum capacity, isincremented onto the current value of the recharging counter.Illustrated by section 15, the charging of the batteries up to the fullycharged condition then ensues, represented by the value 0 of therecharging counter. This full charging advantageously ensues withmaximum current, since, of course, the maximum capacity and the requiredcharging of the batteries are now known and overcharging therefor neednot be feared.

If other batteries then happen to be utilized in turn, these exhibitinga lower maximum capacity, an empty condition of the batteries is againachieved due to operation of the device, at 16, given a lower value ofthe recharging counter at 17, this being stored again as current valuefor the following charging phase, likewise again with the 10%incrementation for compensating the time span of the deactivation.

Another possibility for learning a new capacity is established when thedevice is turned off and the recharging counter signals a highercapacity level than in the prior condition. This version is shown in thediagram of FIG. 3.

The point of departure is again a fully charged condition of thebatteries at 21, whereby the value of the recharging counter thenincreases in the region 22 due to use of the device, this beingidentified via current balancing. The device is then shut off at 23.Before the shut-off, the maximum capacity stored in theEEPROM—represented by the part of the dot-dashed line preceding thesection 23—is compared to the content of the recharging counter. Whenthis, as in FIG. 2, is higher, then this value of the recharging counteris stored as new maximum capacity and the following charging phase withmaximum current is implemented up to the value zero of the rechargingcounter at 24. Here, too, the preceding incrementation of 10% of themaximum capacity again advantageously ensues.

After the fully charged phase and longer operation, the device is thenshut-off again at 25. Since, however, the value of the rechargingcounter is lower here than the stored value for the newly learnedmaximum capacity, this is not modified and no new value is stored. Thesubsequent charging of the batteries up to the maximum capacity againensues—following 10% incrementation—from the current value up to thevalue zero of the recharging counter.

FIG. 4, finally, shows as to how a new capacity of batteries can belearned. Fully charged batteries, at most with maintaining charge, at31, again form the basis. Given operation of the device in section 32,the recharging counter is incremented and, finally, at 33, is connectedto the charging device without a discharge condition of the batterieshaving been previously achieved. Since, however, the value of therecharging counter at 33 is higher than the previously stored maximumcapacity, this new value is stored as new maximum capacity, this beingsymbolized by raising the dot-dashed line to a higher level.

Before, however, the following charging phase with complete charging ofthe batteries has been ended, the device is separated from the chargingdevice and is placed back into operation, this being represented by theincrease of the recharging counter in section 34 from a value unequal tozero up to a value at 35, this value lying above the maximum capacity.Since, however, fully charged batteries did not form the basis, one ofthe criteria for the learning method according to the invention was notestablished, so that the new value of the recharging counter is notstored as new maximum capacity and this, thus, remains unmodified.

In a following, full charging phase 36, thus, charging is carried outfrom the current value of the recharging counter up to the value zerowith maximum current. Since the device was also not shut off, nocompensatory incrementation as in the preceding examples ensues, either.

The above-described features for recognizing the capacity and thecharged condition of newly inserted batteries can be realized as a fixedcircuit but also, preferably, as a software version.

Finally, let it also be mentioned that a monitoring of individualparameters during charging is needed in addition to the measurement ofthe charging current already explained above, since, given overchargingof the batteries with a maximum current, the battery temperature and,thus, the internal cell pressure increase, in response whereto damage tothe cells with deterioration of the service life and of the capacity upto destruction can occur.

The maximum charging voltage is thus followed-up for instance duringfull charging. When the charging voltage in turn drops by a specificamount, the procedure is aborted after a predetermined time span ofcontinuous downward transgression, for example five minutes. During theinitial time of full charging, for instance the first five chargingminutes, when switching the charging current (for example, temperaturemeasurement) and during normal charging, what is referred to as this “dUrecognition” is turned off; otherwise, it is always active as soon ascharging is carried out with maximum intensity of current. This occursin order to prevent misconnections given voltage elevations at the startof charging or drops in voltage when switching off the charging current.When the charging voltage drops as a result of a change in load (forexample, given a call, conversation, display illumination, etc. in thecase of, for example, mobile telephones), then the maximum chargingvoltage is correspondingly corrected down.

A further protective measure is the temperature monitoring shown indiagram form in FIGS. 5a and 5 b. Temperature thresholds includinghysteresis are defined for this purpose. When, during charging withmaximum current, the upper value of one of two lower thresholds isreached, a switch is made to half the charging current. This can againbe realized in a simple way by alternately charging with maximum currentfor a specific time span and subsequent interruption of charging for thesame time span. When a second, upper threshold is reached, a switch ismade to maintaining charging with, preferably, one-sixth of the maximumcurrent and the current balancing is also switched off. This reductionin current given even increasing temperature is shown in FIG. 5a.

When the temperature subsequently sinks in turn, then charging with halfthe charging current as well as the current balancing are re-activatedwhen the lower, second threshold is reached, as shown in FIG. 5b. When,following a further reduction in temperature, the lower, firsttemperature threshold has also been reached, the charging current,finally, is re-boosted to the maximum value for accelerated charging. Apotential dU recognition must be suspended in all current switchingevents.

The battery temperature is preferably determined at specific timeintervals, for example every five minutes whereby each measuring eventcontains a registration of 40 temperature values with subsequent,arithmetic averaging.

Finally, a reliable recognition of the discharged condition of thebatteries shall also be discussed. A voltage window is defined aroundthe previously determined reference value for the discharged condition,usually 2.28 V. The discharge curve gradient is determined therein, forexample in a measuring grid having a spacing of one minute in order toreport the discharge condition of the battery dependent on the batteryemployed in the voltage bend of the discharge curve, which ensues givena curvature of the discharge curve (second derivation).

The discharged condition is reported either when the lower limit of thewindow area has been reached or when the voltage lies in the windowarea, the gradient of the discharge curve is more negative than apredetermined value (in voltage drop-off/time), and the gradient wasmore highly negative than before a pre-determined number of times insuccession, for example three times.

Given load changes, for example, for instance a call, conversation,etc., the last-described counting is reset because the dischargedcondition would otherwise be incorrectly signaled. Here, namely, thereis a left-hand curvature of the discharge curve, whereas the dischargedcondition is to be reported given a right-hand curvature. The countingis also reset when the gradient no longer becomes more highly negative,whereby there is no longer a right-hand curvature or a mismeasurement.

What is claimed is:
 1. A method for charging batteries, particularly incordless communication devices, said method comprising the steps of:inserting at least one battery into a device for a first time; aftersaid insertion, during an initial charging phase, fully charging saidbattery; after said full charging, at least partially discharging saidbattery; generating at each point in time a value representing acapacity drawn up to said partial discharging; after said partialdischarge, given a start of a renewed charging phase, comparing saidgenerated value to a stored base value representing a duration of saidinitial charging phase; and after said comparison, during subsequentcharging phases following said initial charging phase, at leastpartially charging said battery when said generated value is one of lessthan or equal to said base value and when said generated value that,over and above this, is stored as a new base value when said generatedvalue is higher than said base value hitherto stored and said batterieshave a fully charged condition at a beginning of a discharge phaseleading to said generated value.
 2. The method according to claim 1,further comprising the steps of: following said initial charging phase,fully discharging said battery; generating a value representing a drawncapacity from said fully discharging; and during subsequent chargingphases following said initial charging phase, at least partiallycharging said battery dependent on a generated value that, over andabove this, is stored as a new base value when said generated valuedeviates from said base value and said batteries have a fully chargedcondition at a beginning of a discharge phase leading to said generatedvalue.
 3. The method according to claim 1, wherein a duration of saidinitial charging phase and, thus, said base value is initiallyprescribed dependent on a maximum capacity of said initially usedbattery.
 4. The method according to claim 1, further comprising thesteps of: establishing said base value as a value of a rechargingcounter, said recharging counter being de-incremented proportionally toa product of a charging current measured during said charging phases andtime; and establishing said value generated on said basis of said drawncapacity as a value of a recharging counter, said recharging counterbeing de-incremented proportionally to said product of said chargingcurrent measured during said charging phases and time.
 5. The methodaccording to claim 4, further comprising the step of: depositing saidfirst, predetermined base value and each generated value of saidrecharging counter to be stored in an EEPROM.
 6. The method according toclaim 1, wherein said battery is charged with maximum current in a firstpart of said initial charging phase for about 5.5 hours; and whereinsaid battery is charged with lower current of about half said maximumcurrent in a remaining part of said initial charging phase.
 7. Themethod according to claim 1, further comprising the step of: setting acondition in said device allowing an overwriting of said base value onlyupon condition of one of when a complete initial charging phase has beenrun, when a value generated on a basis of said at least partialdischarge of said battery is higher than one of said base value, andwhen a value generated on a basis of said complete discharge of saidbattery deviates from said base value and said generated value lieswithin predetermined limits.
 8. The method according to claim 7, furthercomprising the step of: establishing said condition allowing saidoverwriting of said base value by an initial charging flag reset in anEEPROM.
 9. The method according to claim 1, further comprising the stepsof: preceding said initial charging phase and after said insertion ofsaid battery into said device for a first time, determining a voltage ofsaid battery; comparing said determined battery voltage to a lowervoltage threshold and to a second, predetermined voltage value; andgenerating a first display status when said determined battery voltageis lower than said lower voltage threshold; generating a second displaystatus when said determined battery voltage is one of lower than orequal to said second, predetermined voltage value; and generating athird display status when said determined battery voltage is higher thansaid second, predetermined voltage value.
 10. The method according toclaim 9, further comprising the step of: averaging said second voltagevalue from a predetermined voltage value that represents a dischargedcondition of said battery and a voltage value stored in an EEPROM thatrepresents a maximum charging voltage of previously employed batteries.11. The method according to claim 9, further comprising the steps of:following said initial charging phase, comparing a currently generatedvalue representing a previously drawn capacity to said base value for amaximum capacity to be drawn; generating a fourth display status whensaid determined battery voltage is lower than said lower voltagethreshold; and generating a number of further display statusesrepresenting a charging condition of said battery dependent on arelationship of a current, generated value to said base value.
 12. Themethod according to claim 11, wherein said first display status isgenerated during every charging phase following said initial chargingphase when said current, generated value is between 0% and 33% of saidbase value; wherein said second display status is generated when saidcurrent, generated value is between 34% and 66% of said base value;wherein said third display status is generated when said current,generated value is between 67% and 99% of said base value; and furthercomprising the step of: generating a fifth display status when saidcurrent, generated value is equal to said base value.
 13. The methodaccording to claim 1, further comprising the steps of: monitoring acharging voltage curve during each charging phase implemented withmaximum current; and ending said charging when said charging voltage hascontinuously dropped below a previously achieved value over a specifictime span.
 14. The method according to claim 13, further comprising thestep of: suspending said monitoring of said charging voltage curve at abeginning of charging during a predetermined time span, given potentialswitching of said charging current and during charging phases followingsaid initial charging phase.
 15. The method according to claim 1,further comprising the steps of: monitoring a temperature of saidbattery during charging; and prescribing at least two temperaturethresholds comprising a lower temperature threshold and a highertemperature threshold having a value greater than said lower temperaturethreshold; wherein said battery is charged with full charging currentbelow a lower temperature threshold; wherein said battery is chargedwith half said charging current between said lower temperature thresholdand said higher temperature threshold; and wherein said battery ischarged during a maintenance charging with one-sixth of said fullcharging current above said higher temperature threshold.
 16. The methodaccording to claim 15, wherein each temperature threshold is in turndivided into two sub-thresholds comprising a lower sub-threshold and ahigher sub-threshold having a value greater than said lowersub-threshold, wherein in a case of rising temperature of said battery,an intensity of said charging current is switched at a highersub-threshold of a respective temperature threshold and, in a case ofdropping temperature, said intensity of said charging current isswitched at a lower sub-threshold of a respective temperature threshold.17. The method according to claim 1, further comprising the step of:monitoring a discharge curve of a voltage associated with said charging;and generating a first display status during one of: when said voltagelies in a range around a value representing a discharged condition ofsaid battery, when a gradient of said discharge curve exceeds apredetermined, negative value, and was more highly negative for apredetermined plurality of times in succession, and when a lower end ofa range around a value representing said discharged condition has beenreached.